It can also be a period that can vary in length each month from anywhere between 1 or 2 days and a week.  A woman who experiences variations of less than eight days between her longest cycles and shortest cycles is considered to have regular menstrual cycles. It is unusual for a woman to experience cycle length variations of less than four days. Length variation between eight and 20 days is considered as moderately irregular. Variation of 21 days or more between a woman's shortest and longest cycle lengths is considered very irregular.   More Science...

Whilst an irregular menstrual cycle is not a problem in itself, it does make timing sex much more difficult.  A woman has the best chance of conceiving a child in the 3 days leading up to ovulation. More Science...

Whilst irregular periods can cause problems getting pregnant, it doesn't mean having a baby is not an option.  It all depends on what is causing the irregular periods, how infrequent they are and whether it’s possible for sex to be timed so as to improve the chances of conceiving a baby.  While it’s possible some women may need to use assisted reproduction techniques, this is by no means definite.  More Science...

Irregular periods are not normally a problem - until a woman tries to conceive.  During a normal cycle, conception can only occur if the egg meets the sperm within 24 hours of ovulation.

Irregular periods can therefore reduce the chance of pregnancy because it is not always possible to predict when ovulation will occur and because ovulation may not always occur.  If hormonal imbalances are the reason for the irregular periods, a fertilised egg might not be able to implant in the uterine wall and the woman might not produce the hormones required to support a pregnancy if one does result.  More Science...

Irregular periods may be temporary and can be caused by stress or illness.  In these cases, cycles should settle down over time.  More Science...

Stress is a common cause of irregular periods.  Women who are fatigued, worried, or anxious can end up with unbalanced hormones.   More Science...

A poor diet or extreme weight loss or gain can affect hormone levels. Women with anorexia or bulimia often have no period or irregular periods.  More Science...

Thyroid disorders can cause irregular periods if blood levels of the thyroid hormone go too low or too high. Other health conditions that may cause an irregular cycle include sexually transmitted diseases, diabetes, fibroids, eating disorders, and endometriosis.  More Science...

Intense exercise can wreak havoc on the body, often causing irregular periods. More Science...

This occurs when a hormone imbalance interferes with normal ovulation and is a major cause of infertility. As well as irregular periods, common symptoms include weight gain, acne, male-type hair growth on the face and body, and raised insulin levels.  More Science...

An anovulatory cycle is a menstrual cycle during which the ovaries do not release an oocyte. Therefore, ovulation does not take place. However, a woman who does not ovulate at each menstrual cycle is not necessarily going through menopause. More Science...

Oligovulation is infrequent or irregular ovulation (usually defined as cycles of ≥36 days or <8 cycles a year). More Science...

Women who consume caffeine are more likely to have shortened menses.  The basis for this is that caffeine restricts blood vessels, reducing uterine blood flow. Consequently, this leads to a decrease in menstrual bleeding and a shortened cycle, resulting in the variability and irregularity of a woman's period.  More Science...

Doctors may prescribe the fertiliy drug, Clomid to correct infrequent ovulation by stimulating the hormones. More Science...

For overweight women with polycystic ovary syndrome (PCOS), the symptoms can be improved by losing weight, which will also help with irregular periods. By losing weight, the body does not need to produce as much insulin, which reduces testosterone levels and improves the chance of ovulation (releasing an egg each month). More Science...

Treatment for an overactive thyroid aims to return the level of thyroid hormones in the blood to normal.  Women may need to take medication to stop the thyroid gland producing too many hormones. More Science...

Stress or sudden weight loss may be diagnosed as a cause of irregular periods. Relaxation techniques, stress management or counselling (talking to a therapist) may be recommended.  More Science...

If excessive caffeine is believed to be an issue, women should reduce their caffeine intake over several weeks.  Health studies have shown that increased amounts of caffeine do indeed lower a woman's chance of conceiving, and she doesn't necessarily have to drink more than a couple of cups per day.  More Science...